The human cornea will be tested for its ability to appreciate hot and cold sensations by stimulating it with a jet of saline at different temperatures. A jet of saline, appropriately modified, will be used to search for touch, temperature and chemical receptors by electrophysiological methods in isolated rat corneas. Attempts will be made to stimulate the epithelial cells and the nerve receptors separately with very small stimulating sources in order to find if nerve excitation is mediated by the cells. The role of acetylcholine in excitation will be examined. The mechanisms underlying the excitation process will be studied by experiments on the interaction of various modalities at the subthreshold level. Evidence of axonal transport in the trigeminal nerve will be looked for, and attempts to interrupt it by pharmacological means will be made to find out if this could play a role in the etiology and neurotrophic keratitis.